Excess Free Light Chains in Serum Immunofixation Electrophoresis: Attributes of a Distinctive Pattern

Serum and urine protein electrophoresis and immunofixation are essential for identification and categorization of M protein/monoclonal protein. Based on the number of discrete bands identified the condition can be a monoclonal, biclonal or triclonal gammopathy. A subset of cases show an interesting pattern on immunofixation electrophoresis, with a complete immunoglobulin molecule, along with excess free light chains where in one light chain band shows similar mobility as the heavy chain, while the other light chain band of same isotype has a different mobility. Over a 3 year study period, 420 immunofixation electrophoresis gels were studied to select the cases with the typical pattern as described. The clinical records where searched for data of baseline evaluations done prior to starting therapy, including clinical presentation, biochemical parameters, hemogram and bone marrow examination. Twenty cases (4.7%) were identified from the records, of these 77.8% cases had renal impairment and 33.3% presented with rapidly progressive renal failure. The possible explanation is the toxic effects of excess free light chains, in our cohort. The bound LCs show mobility similar to the HC bands on serum immunofixation gels, however the free light chains, exist in polymeric forms and show a different mobility. The identification and reporting of this pattern provides additional information regarding the high load of light chains, and indicates that patient may have a poor renal outcome/performance.